Once the specific situation is for all intents & purposes is resolved for the poster, there's no reason the etiquette question can't be discussed in general terms after that.
Ah, but that's not thread drift. It's still the same etiquette question being discussed. I'm referring to things like:
"(On topic discussion), and by the way, I saw something like that on 'X Files' once."
"X Files is the best! Did you see the one they filmed in Albuquerque?"
"I live in ABQ, and got Duchovny's autograph!"
Followed by two or more pages of talk about X Files. Then someone makes an on topic post, but the next 5 posters continue the off-topic discussion. This is rather rude to the people who want to read about the original question, or are waiting for an update. They have the choice to either drop off, or page through what is, to them, a lot of nonsense.
Better to say, "X-files is the best! Let's talk about it over in the Coffee House! I'll make the first post!"
It can also happen in more natural ways. For instance, the original post about TP and her SS behavior at Easter dinner drifted into a discussion about proper manners around vegans and vegetarians. That's not too far off topic, but it's still off topic.
I am most fervent',
Your friend and servant,